1. Field of the Invention
The present invention relates to a method of preparing dimeric fatty acids and/or esters thereof from unsaturated monomeric fatty acids and/or esters thereof. More particularly, the invention herein relates to a method of preparing dimeric fatty acids and/or esters thereof having a relatively low residual content of interesters, and to the dimeric fatty acid and/or dimeric fatty ester product which can be used to prepare higher molecular weight polymers than that obtained by polymerizing dimeric fatty acids and/or esters thereof with higher interester content.
2. Brief Description of the Prior Art
It is known that monomeric unsaturated fatty acids and the alkyl esters of these fatty acids can be utilized to manufacture dimeric fatty acids and dimeric fatty esters, which in turn, can be used to manufacture polyamide, epoxy and polyester resins for use, inter alia, in thermographic inks and coatings for plastic films, papers, and paperboard. Production of dimeric fatty acids and their esters typically comprises heating monomeric unsaturated monocarboxylic acids and/or their alkyl esters having from about 11 to about 24 carbon atoms, e.g., oleic acid, linoleic acid, esters of these fatty acids and the like, in the presence of a mineral clay and water, as described, e.g., in U.S. Pat. Nos. 3,632,822, 3,422,124, 2,793,219, 2,793,220, 2,955,121, and 4,776,983, the contents of each of which are incorporated by reference herein. A typical end product of these methods is a 36-carbon dicarboxylic dimeric fatty acid or ester thereof. Dimeric fatty acids can also be produced from dimerizing dicarboxylic acids and combinations of mono- and dicarboxylic acids as described, e.g., in U.S. Pat. Nos. 5,001,260 and 4,895,982, the contents of each of which are incorporated by reference herein.
Such methods of preparing dimeric fatty acids and dimeric fatty esters also result in the formation of one or more interesters, which result from the reaction of a double bond of an unsaturated fatty acid and ester thereof with water to form an alcohol which in turn reacts with a mole of acid to form interester. The presence of interesters in the dimeric fatty acid and fatty ester product has been found to hinder the formation of more desirable higher molecular weight polymers when the dimeric fatty acids and esters thereof are polymerized. Interesters cannot be readily removed from the dimeric fatty acids or their esters by simple methods, e.g., distillation, stripping, etc. Accordingly, an efficient, low cost method of preparing dimeric fatty acids or dimeric fatty esters of substantially reduced interester content is highly desired.